Some forms of anxiety and affective disorder, such as panic disorder and major depression, appear distinct, while other forms, such as generalized anxiety disorder and chronic depression or dysthymia, may lie on a continuum and blend with each other. However, even panic disorder and major depression have many common features. Moreover, for reasons not yet clear, they occur together frequently, and their combined occurrence in the same patient has been associated with greater severity and chronicity, decreased treatment responsiveness, and, possibly, increased familial prevalence of anxiety and/or depression. Finally, studies of primary care patients suggest the frequent occurrence of a mixed anxiety-depressive disorder that may often be subsyndromal by DSM-III-R criteria but is nevertheless associated with prominent distress and/or impairment.